I slightly prefer Imogen, but here are my thoughts:
Imogene makes me think "I'm a gene..." like something DNA would say to start a conversation at a particularly slow party...
Imogen makes me think "I'm a gin..." which is what DNA says at same party after a few too many drinks...

Thanks for the imput everyone! Our DD was born on July 4 and we did name her Imogene.

Curiousity has me wondering if people are pronouncing it differently than we do though.

We pronounce it the only way I've ever heard - which is with a SHORT "I" sound. Now that we've named her though, I've met a few people who assume it is a LONG "I" (like EYE-mo-jean). To me that is totally weird and I've never heard it that way before.